AC coupling capacitors are used when receiving signals from off-chip elements, typically at inputs to high speed signal networks and have the property of preventing DC currents as well as affecting certain signal transient behaviors. Commonly most AC coupling capacitors are placed as discrete components on circuit cards as close as possible to the terminus of the network at a receiving device. External components are typically tested at card test using circuit in place (CIP) and/or another electrical network test, e.g., using a chip test resource such as an I.E.E.E. testing protocol 1149.6 (e.g., boundary scanning).
High speed chip receivers have recently begun to integrate the AC coupling capacitor in the chip itself, e.g., located in series circuit connection with a chip terminal. The problem introduced by integrated AC coupling capacitors is a loss of coverage in the manufacturing process flow. Formerly at card test a “bad” capacitor can readily be reworked. Discovering a bad capacitor at card test, where the AC coupling capacitor is integrated into the chip, requires the removal, redressing and replacement of the chip which is significantly more expensive than replacing a capacitor component.
Off chip manufacturing solutions for testing integrated capacitors are known and depending on the circuit configurations traditional CV or charge time capacitor testing can be performed. However, manufacturing equipment does not typically have capacitor test systems available on a per pin or per differential pin pair basis. If the chip does incorporate into its design support for the 1149.6 IEEE standard, then it is possible to program automated manufacturing test equipment to provide stimulus where on-chip logic produces a logic result which tests for the presence of integrated AC coupling capacitors in the receivers. However, detecting the presence of a capacitor(s) does not provide any other detail than that a capacitor is, or is not, in the signal path.
Additionally, advances in integration have led to chips having many high speed signal I/O making the problem even more difficult to solve in the manufacturing test environment. Most manufacturing test environments are incapable of testing advanced high speed serial busses at-speed.
Manufacturing test equipment currently does not support the ability to check for the presence and a relative magnitude of integrated, on-chip AC coupling capacitors.